The origins of the 260 day ritual year are not known for certain, but there are a couple of hypotheses:

1. Pregnancy. 260 days is roughly the gestation period of a baby, so this may have been the inspiration for tracking this duration. (For what it is worth, modern Maya timekeepers cite this as being the reason for the length of the 260 day ritual calendar.)

2. In the tropics there are two days of the year when the Sun passes through the zenith and objects cast no shadows. In the latitude where the earliest Mesoamerican civilizations emerged, the length of time between these two days of the year is about 260 days.

3. Numerology. 260 is the product of 20 and 13. 20 was significant in Mesoamerican culture because it was the base of their numbering system and was associated with the human body (given that we have 20 fingers and toes). And the number 13 was associated with the cosmos. So the number 260 represented a kind of interlocking between the human and the cosmic.

It's also worth noting that the Maya also tracked a 365 solar cycle, so they did have a concept of a more standard kind of "year." The 365 cycle was used for civil purposes. The 260 day ritual cycle was used more for divination.

(Shameless plug, but if you want to learn more about Mesoamerican astronomy I have a podcast about the history of astronomy and I talked about it on the last episode: https://songofurania.com/episode/047)